The present invention relates generally to packet data communication systems and, more particularly, to a method and apparatus for dynamic transmission resource allocation.
The growth of commercial communication systems and, in particular, the explosive growth of cellular radiotelephone systems, have compelled system designers to search for ways to increase system capacity without reducing communication quality beyond consumer tolerance thresholds. At the same time usage of mobile communication equipment for transmission of data rather than speech has become increasingly popular by consumers. The possibility to send and receive electronic mail and to use a web browser to obtain world-wide-web access is frequently discussed as services that will be more and more used in wireless communication systems. As a response to this, communication system designers search for ways to efficiently transfer data information to and from mobile users.
There are fundamental differences between requirements for data communication and e.g., speech communication. For example, delay requirements are higher for speech, which is a real time service, and the error requirements are higher for data communication, while the delay constraints are lower. The use of packet data protocols, which are more suitable for transmission of data than circuit switched protocols, starts to find its way into cellular communication systems. Packet service integration in both GSM cellular systems as well as DAMPS cellular systems is presently being standardized.
Today, GSM systems provide a circuit switched data service, which can be used to interconnect with external data networks. The circuit switched data service is used for both circuit switched as well as packet switched data communication. To make packet switched data communication more efficient, a new packet switched data service called GPRS (General Packet Radio Services) is introduced as a part of GSM. GPRS will allow for packet switched communication e.g., IP or virtual circuit switched communication. GPRS will support both connectionless protocols (e.g., IP) as well as a connection-oriented protocol (X.25). One of the advantages with a packet switched data communication protocol is that a single transmission resource can be shared between a number of users. Thus, in the case of e.g., a GSM cellular system, a timeslot on a radio frequency carrier can be utilized by several mobile users for reception and transmission of data. The shared transmission resource is managed by the network side of the cellular system both for downlink and uplink transmissions.
GPRS is a GSM service and parts of the GSM infrastructure will be used. Those parts of the GSM communication system are described in European Telecommunication Standard Institute (ETSI) document ETS 300 574 which is incorporated by reference herein.
An advantage of introducing a packet data protocol in cellular systems is the ability to support high data rate transmissions and at the same time achieve a flexibility and efficient utilization of the radio frequency bandwidth over the radio interface. The concept of GPRS is designed for so-called xe2x80x9cmultislot operationsxe2x80x9d where a single user is allowed to occupy more than one transmission resource simultaneously.
An overview of the GPRS network architecture is illustrated in FIG. 1. Information packets from external networks 122, 124 will enter the GPRS network at a GGSN (Gateway GPRS Service Node) 120. The packet is then routed from the GGSN via a backbone network, 118, to a SGSN (Serving GPRS Support Node), 116, that is serving the area in which the addressed GPRS mobile resides. From the SGSN the packets are routed to the correct BSS (Base Station System), in a dedicated GPRS transmission. A GPRS register, 115, will hold all GPRS subscription data. The GPRS register may, or may not, be integrated with the HLR (Home Location Register) 114 of the GSM system. Subscriber data may be interchanged between the SGSN and the MSC to ensure service interaction, such as restricted roaming.
FIG. 2 illustrates packet transformation flow for a GPRS system. This is also briefly described in D. Turina et al., xe2x80x9cA Proposal for Multi-Slot MAC Layer Operation for Packet Data Channel in GSMxe2x80x9d, ICUPC, 1996, vol.2, pp.572-576, which is incorporated by reference herein.
The packets which are received from the network, 210, are mapped onto one or more logical link control (LLC) frames, 212, containing an information field, a frame header (FH) and a frame check sequence (FCS). An LLC frame is mapped onto a plurality of radio link data blocks (RLC data blocks) 214, each of which include a block header (BH), information field and block check sequence (BCS), which can be used in the receiver to check for errors in the information field. A block, as is recognized by those skilled in the art, is the smallest part of the packet which is re-transmittable over the air interface. The RLC blocks are further mapped onto physical layer radio blocks. In a GPRS system, one radio block is mapped onto four normal bursts sent consecutively on one GSM physical channel.
The block header includes an Uplink State Flag (USF) field to support the dynamic medium access method on the uplink. The USF is used in a packet data channel to allow multiplexing of radio blocks from a number of mobile users, i.e., dynamic allocation of shared transmission resources in the uplink. The USF contains 3 information bits allowing for coding of eight different USF states which are used to multiplex the uplink traffic. The USF is included in the beginning of each radio block transmitted in the downlink, i.e., interleaved with downlink traffic to a specific mobile user. Since the USF is transmitted in every radio block in the downlink, all mobiles that use the dynamic allocation method and share a certain transmission resource must, therefore, always listen to the downlink channel to determine whether the USF indicates free uplink transmission for any of the mobiles. If a mobile user is indicated by a USF, transmission in the uplink is allowed in the next uplink radio block. This technique is illustrated in FIG. 3, where USF=R1 indicates that mobile 1 (MS1) may use the following four bursts to transmit in the uplink. In the case of multislot assignment, when a mobile is assigned more than one timeslot in each TDMA frame, more than one RLC block may be transmitted during four TDMA frames, however, every single RLC block is always interleaved over four bursts on one physical channel, i.e., timeslot. Then, according to FIG. 3, if the USF=R2, this indicates that mobile 2 (MS2) may use the following four bursts to transmit in the uplink. The value xe2x80x9cFxe2x80x9d denotes a Packet Random Access Channel (PRACH) which is used by the mobile users to initiate uplink transmissions.
A drawback with the above-described protocol becomes apparent when considering the use of adaptive antenna arrays which increase cellular system capacity and efficient usage of scarce radio resources. The implementation of antenna arrays can allow for more efficient transmission and reception of radio signals, since the transmitted energy can be directed towards a certain receiver in antenna lobes. This significantly limits the overall interference level in cellular systems and transmitted output power may be decreased and limited to certain directions from e.g., a base station transmitter.
It is of great importance for increases in capacity of future cellular systems that such adaptive antennas be utilized efficiently. There are, however, limitations to the performance gain achieved by implementing adaptive antennas if, for example, downlink traffic directed to a specific mobile user is interleaved in the same bursts as downlink control signaling intended for other users. One example is the above-mentioned USF flag being included in downlink transmissions to a specific user. Different mobiles may be geographically distant and it is then impossible to concentrate the transmitted signal energy to only one or a few directions. It is similarly difficult to obtain an efficient power control algorithm for transmissions directed to more than one mobile user.
One other drawback with the described protocol is the (non-)possibility of introducing new modulation for certain radio blocks on downlink. Namely, the newest development in GSM suggests usage of a new higher level modulation for users with good radio conditions which then can increase the user data rate and the system throughput in general. It would be advantageous to be able to freely multiplex radio blocks using the existing and the new modulation on the downlink thus obtaining the trunking gain. In the current protocol, it is not feasible in the situations where one GPRS mobile station is monitoring the USF that has to arrive in the radio block that uses the existing modulation.
One possibility to overcome this drawback is to use a fixed allocation medium access method, where the initial setup signaling would specify when users are allowed to transmit on the uplink. There are, however, advantages with having a dynamic multiplexing in the uplink due to e.g., an increased flexibility in allocation of transmission resources.
It is an object of the present invention to increase efficiency in a packet data communication system employing a dynamic resource allocation method by introducing additional flexibility in multiplexing of uplink transmission resources. By using an USF in the downlink to indicate that a mobile is scheduled to transmit an arbitrary number of consecutive radio blocks on a physical channel, the mobile does not have to listen for the USF during a number of following downlink blocks, a number based on the indication given in the channel assignment message to that particular mobile station.
The determination of what a reception of a USF indicates to the mobile station using an uplink assignment is specified in the initial signaling when assigning a transmission resource, i.e., a physical channel. In a TDMA system a physical channel may be a timeslot. In multislot systems, several timeslots may be allocated, but there will be different USF values assigned for every allocated timeslot, which may or may not indicate the same number of consecutive radio block transmissions in the uplink. Furthermore, one appearance of USF may indicate a different number of uplink radio block transmissions to different users depending on the individual channel assignments. By scheduling transmission of an arbitrary number of consecutive radio blocks for uplink transmission on a physical channel, there is no need for a mobile user to listen for USFs during that transmission, before the last uplink radio block scheduled. As a result, the transmission in the downlink can, e.g., by way of adaptive antennas and power control algorithms, be performed more efficiently and an overall interference decrease may be achieved.
The above objects and features of the present invention will be more apparent from the following description of the preferred embodiments with reference to the accompanying drawings, wherein:
FIG. 1 illustrates a GPRS network architecture;
FIG. 2 illustrates a packet transmission flow and information mapping in an exemplary packet data communication system;
FIG. 3 illustrates an USF flag indicating uplink transmission multiplexing;
FIG. 4 illustrates uplink transmission multiplexing performed by a USF indicating transmission of one uplink radio block;
FIG. 5 illustrates uplink transmission multiplexing performed by a USF indicating transmission of more than one uplink radio block; and
FIGS. 6A and 6B illustrate an exemplary traffic situation in a packet data communication system according to the present invention.